The present invention relates to a steering angle detecting system for automotive vehicles, and more particularly to a steering angle detecting system which has improved reliability in detecting a steering angle.
Recently, some four-wheel automotive vehicles incorporate a control system for carrying out given control in response to the steering angle. Such a control system includes a steering angle detecting system which uses a steering angle sensor for detecting the steering angle.
The steering angle sensor of the steering angle detecting system is usually constructed such that a signal indicative of the steering angle is generated by means of pulses. For instance, the sensor comprises optical pulse-generating means, which generates optical signal pulses in accordance with rotation of a steering wheel when the driver operates the steering wheel, whereby information on the steering angle of the vehicle is obtained by means of a counter which counts signal pulses based on the optical signal pulses. The steering angle detecting system thus constructed using the steering angle sensor has the advantage that, since pulses are used as a processing signal in the sensor, the steering angle can be resolved to a desired high degree to thereby enhance precision in detecting the steering angle.
However, in the event that abnormality occurs in the pulse generating means or in the pulse processing section of the steering angle detecting system, it will be impossible to carry out proper control in response to the steering angle. Therefore, to detect abnormality in the steering angle detecting system is essential for prevention of malfunctioning of the control system due to the abnormality. In particular, if the steering angle detecting system is constructed such that the number of generated pulses indicates the steering amount, i.e. the steering angle through which the steering wheel has been rotated, abnormality, such as miscounting of signal pulses due to omission of signal pulses or superposition of noise on signal pulses, results in that the counter output indicates a steering amount different from the actual steering amount. Therefore, it is critically important to properly detect such an abnormality.
Further, an abnormality, which should result in a sudden change in the signal indicative of the steering angle, such as malfunctioning of the counter, suddenly affects the operation of the control system. Therefore, it is particularly important to promptly detect the abnormality.